The present invention relates to a parts feeder (a vibration-type parts feeder) attached to and employed in a resistance spot welding machine, and further in detail, relates to a parts feeding method and a device for sorting right and wrong positioning of projection nuts that have projections (projections for welding) formed at four corners thereof and other similar small parts (hereinafter, welding nuts).
As shown in FIGS. 13 through 15, up to this time, a generally known nuts feeding method and nuts feeding device have been such that, when welding nuts N having projections for welding P are lined up and fed continuously on a transportation track 31 which stands up spirally from a bottom portion of a vibration bowl 30, it is judged whether each of the welding nuts is upward or downward by the way that the welding nuts go up along the transportation track 31, nuts whose projections are downward (normal positioned parts) and whose projections are upward (abnormal positioned parts) pass on a toothed track 34 for selecting upward or downward nuts, and only the normal positioned parts are transported to a feeder unit (a head for supplying nuts) which is attached to a spot welding machine.
A method for selecting upward parts or downward parts and a corresponding device in the prior art have the toothed track 34, in which several teeth are formed along a direction that the parts move, connected in series to an end portion of the transportation track 31.
In this case, as shown in FIGS. 13 and 14, the normal positioned parts move along guide rails 32, 33 consisting of large and small metal round bars, and are advanced and are transported to a parts transportation opening in a condition that projections P of the welding nuts N are engaged with the teeth when the nuts go over the toothed track 34.
On the other hand, as shown in FIG. 15, because a flat surface 35 at an upper portion of the nut is not engaged with tooth grooves 36 when the projections P are inverse (upward), the nuts fall into the vibration bowl to collect. Then, the nuts go up along the transportation track 31 again.
Although not shown in the figures, nuts selected and arranged normally are transported to a rail extending to an outside of the bowl and are separated individually by a separation device along the way. The separated nuts are supplied to the feeder unit by being blown into a supply hose by compressed air injected from an air nozzle.
The welding nut transported to the feeder unit is stopped in the feeder unit. The stopped nut is held at an end of a spindle by driving the spindle so as to supply the welding nut forwardly from the feeder unit. The welding nut held by the spindle is removed form a stopper position by an advance of the spindle to be supplied to a workpiece positioned on a lower electrode.
The supplied welding nut is gripped with a workpiece set on the lower electrode by pressing movement of an upper electrode and is heated and melted with the workpiece by applying a necessary pressure between the electrodes and sending an electric current for welding to the projection of the nut to be joined together.
In the prior vibration type welding nuts feeding device, various selection means such as a tooth-shaped track and guide rails consisting of large and small metallic round bars have been adopted.
In the above-mentioned prior art documents, a mechanism for selecting upward and downward surfaces of the welding nuts or a vibration type welding nuts feeding device with a function for sorting is published in JP 60-151821 U, JP 62-074617 U, JP 2000-219314 A and JP 2001-072233 A, but they only disclose a changing of sorting unit or adjusting parts of the unit.
Accordingly, problems to be resolved by the present invention are that cost reduction and a date of delivery can not be achieved because a vibration bowl for exclusive use with every size of the welding nuts is necessary when the outside dimension of the welding nuts is changed in the prior vibration type welding nuts feeding system, for instance, from M6 type nuts to M8 type nuts. A standardized product can not be attained because skill and experience are necessary in order to weld the guide rails of the metallic round bars so as to match a track line in the prior device for sorting upward and downward welding nuts.